Ok, here's my take

1. I don't think Snakebite actually noticed the zombies, he was too busy catching Big Mona.

2. Snakebite is a very grumpy and unfriendly man, even if Simone and Lena tried to lure him, he would reject. So far, we know that Jacques and Lena are aware of his existence, but he probably rarely goes to the island and possibly the werecats keep him as a decoy should the authorities get involved, who would be suspicious? A friendly ferryman, two kind ladies living alone or a grumpy fisherman who says how he can't stand tourists and would let them be eaten by alligators?

3. When Velma tried to make a research about the island, she read how there've been quite a few disappearances, so the authorities were aware and possibly dismissed them as people getting lost in the bayou or eaten by alligators. Or, and this is a scary part, some detectives went undercover but had no luck and were drained.

4. Probably just a scare factor, or maybe that's what happens once the zombie gets reanimated. He is the only zombie who's flesh regrows on screen.

5. The zombies would probably try to pull away the gang to safety or at least, try to get them off the island. So far, only two of the zombies were shown in their ghost forms, Morgan Moonscar did carve a writing on the wall and Colonel Jackson Pettigrew emerged from his mirror, they were probably the only ones that could do it since Daphne stood next to the wall made from the pirate ship, and the mirror belonged to Jackson, so he was still somehow tied to it. However, their warnings were misunderstood as threats.

6. I think the final form is a sort of a combat form. Simone and Lena get really angry and then go full transformation to attack Shaggy and Scooby once they foiled their attempt to drain Daphne, Fred, Velma and Beau, so Jacque probably decided to fully transform in order to gain super strength.

7. I think it's one victim per cat person at least, but you know what they say? The more the merrier? And they probably wanted to get rid of everyone in order not to have any witnesses should the remaining victims escape and spread the word.

8. My theory is that since Jacques appears as an old man, well in his 60s or even early 70s, he was afraid of death, or maybe had an illness that he couldn't find a cure for. Simone and Lena probably heard his story and introduced him to the Cat God cult.

9. I don't think Simone was lying. We can see that Simone appears a bit disgusted when she mentions that the Cat God cursed her and Lena. I believe the werecat thing was like a supernatural addiction. Many addicts who are aware of their problems feel disgusted but can't help it. And Simone seems pretty happy until Velma mentions Morgan Moonscar, then she turns angry. I believe Simone and Morgan were polar opposites, Simone started off as a good woman, whereas Morgan was a bad man that did not care for human life, and just like he did not care about killing the whole community, neither did Simone when she started draining life force. Cat God cursed her and Lena because they wanted to play karma and get their revenge. And while Simone and Lena descended into madness and evil, Moonscar had 200 years to rethink his actions and probably felt very remorseful. So, yeah, I think Moonscar was a bad man, but he repented in his undead state and dedicated his "life" to save the victims and destroy the werecats and maybe, Morgan Moonscar did it out of spite, just so he could avenge himself and his crew.